In the electronics industry a semiconductor die will often be mounted on a leadframe and encapsulated for protection from atmospheric conditions as well as mechanical damage. The leadframe may be inexpensively stamped from a sheet of electrically conductive material such as copper. The finished component is inexpensive when compared with other packaging methods, and quickly produced.
While a simple leadframe may be sufficient for some semiconductor dies, many semiconductor dies often generate heat which must be dispelled. To dispel this heat a heat sink is employed. The heat sink must be thermally conductive to carry the heat from the semiconductor die. Generally a metal is used for this element. This is where problems with current leadframes develop. In order to dispel the generated heat, the heat sink must be in contact with the semiconductor die or coupled thereto by a thermally conductive material. It is conventional practice to form a back metal on a semiconductor die so that the die can be soldered to a heat sink. Current techniques in leadframe technology utilize copper as the leadframe material, having a mounting area on which a die is mounted. Copper provides good thermal conductivity at a low cost and may act as a heat sink or couple the die to the heat sink. While the heat sink effectively carries heat from the die, the coefficient of thermal expansion (CTE) of the die is much less than the heat sink or copper mounting area. This mismatch in CTE may result in damage to the die or the bond holding the die to the heat sink during temperature cycling. In very small devices the differences in the CTE may not result in any damage, but as the size of the die increases, the mismatch in CTE becomes very important.
The problems mentioned above are prevalent in silicon semiconductor dies over 0.150 inches on a side, and are compounded when a gallium arsenide (GaAs) die is employed. GaAs dies are thin and extremely brittle. The CTE mismatch with copper causes breakage of the die as stresses are relieved and differential expansion and contraction occurs. While GaAs dies no larger than 0.050 inches on a side may be mounted on a copper leadframe, larger dies will be damaged. Due to the need for more functionality and more power, small dies are the extreme minority today.
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art.
Accordingly, it is an object of the present invention to provide a new and improved leadframe.
Another object of the present invention is to provide a leadframe having a CTE substantially matched to silicon and GaAs.
And another object of the present invention is to provide a leadframe having good thermal conductivity for high power.
Still another object of the present invention is to provide a leadframe which is relatively inexpensive.
Yet another object of the present invention is to provide a lightweight leadframe.
Yet another object of the present invention is to provide a leadframe which can be employed with GaAs dies.